GENE-EXPRESSION OF MONOCYTE CHEMOATTRACTANT PROTEIN-1 IN HUMAN MONOCYTES IS REGULATED BY CELL-DENSITY THROUGH PROTEIN-TYROSINE KINASE AND PROTEIN-KINASE-C

The present study investigated the signal transduction pathways leadin g to the gene expression for monocyte chemoattractant protein-1 (MCP-1 ) in human monocytes. By Northern blot analysis, MCP-1 mRNA was undete ctable in freshly isolated monocytes, but was induced and reached a ma ximal level at 4 h during culture. The level of accumulated mRNA alter ed with cell density of the monocytes and was highest at a density of 1 X 10(6) cells/ml. Nuclear run-on assay demonstrated that this cell d ensity-dependent expression of MCP-1 mRNA was regulated at the transcr iptional level, and protein tyrosine kinase (PTK) inhibitors, genistei n and herbimycin A, completely abrogated this gene transcription. Immu noblot analysis for phosphotyrosine in whole cell lysates demonstrated gradual increases in tyrosine phosphorylation of 55-, 60-, and 70-kDa proteins during culture. Cell density regulated tyrosine phosphorylat ion of 70-kDa protein in parallel with alterations in MCP-1 mRNA expre ssion. The protein kinase C (PKC) inhibitor H-7 also abrogated the gen e transcription and suppressed tyrosine phosphorylation of 70-kDa prot ein, whereas HA1004, a structural analogue of H-7, did not. These resu lts suggest that MCP-1 gene expression in cultured monocytes is regula ted by the cell density at the transcriptional level and that the sign aling pathways leading to the gene transcription are mediated through PTK and PKC. It is also suggested that PKC activity plays a critical r ole in tyrosine phosphorylation of 70-kDa protein, which may mediate s ignals regulating the cell density-dependent expression of the MCP-1 g ene. (C) 1994 Academic Press, Inc.